In copending application U.S. Ser. No. 746,541, filed Jan. 19, 1991, now abandoned novel adducts of cyclic carbonyl compounds and alkenes and cycloalkenes are disclosed and claimed. These adducts are produced by reacting a cyclic carbonyl monomer having an ene-reactive carbonyl group with an unsaturated hydrocarbon to form a novel adduct having a molecular weight of about 500 or less. These novel adducts are useful as viscosity modifying agents.